Load-bearing Properties of Lithia-based Glass-ceramic for Minimally Invasive Restorations

Objectives: To improve the application load-bearing capacity of lithium-disilicate (LiDi) glass-ceramic via intaglio surface resin infiltration.
Methods: Discs of LiDi (HT-A2 IPS e.maxCAD, Ivoclar Vivadent) were cut from CAD/CAM blocks (ø12×1 mm) and ground to 15 µm finish. Acid etching (5% HF) was performed for 20, 60, or 120 s (n=10/group). A control, not etched group was included. A second batch of samples was acid etched for 120 s followed by resin infiltration: a coupling agent (Monobond Plus, Ivoclar) was applied and kept in vacuum for 10 min, then heat-treated at 140°C for 2h; after cooling, a thin layer of fluid resin (mix of low molecular-weight monomers) or viscous resin (UDMA, Sigma Aldrich) was applied and kept in vacuum for 10min; Light curing for 1 min was performed for the fluid resin. High-temperature-pressure polymerization (200°C for 1h) was used for UDMA. Color coordinates (CIELab) were measured on plate specimens over white and black backgrounds with a coupling agent (glycerol) to calculate the translucency parameter (TP). Characterization of microstructure and composition was performed with SEM and XRD. Load-bearing capacity was determined by piston-on-3-balls biaxial flexural test.
Results: A trend of reduction in load-bearing capacity was observed with increasing etching times. HF acid etching not only erodes the glass matrix, but also reduces the crystal content on the surface, as observed by SEM-BSE and XRD. The viscous UDMA lacked the ability to infiltrate the porosity created by acid etching, reducing both the TP (36 ±3) and the load-bearing (237 ±37 N). The opposite effect was observed when the fluid resin was used, with the infiltrated group showing load-bearing (290 ±13 N) significantly higher than the etched counterpart 120s (267 ±7 N). TP was not affected by fluid resin infiltration or etching time (~44 ±1).
Conclusions: The intaglio surface resin infiltration can enhance load-bearing capacity of LiDi.